using System;
using System.Collections.Generic;
using System.Text;

namespace QiHe.CodeLib
{
    [Serializable]
    public class Set<T> : List<T>
    {
        public Set() { }
        public Set(params T[] items)
            : this()
        {
            this.AddRange(items);
        }
        public Set<T> Clone()
        {
            Set<T> clone = new Set<T>();
            clone.AddRange(this);
            return clone;
        }

        public static readonly Set<T> Empty = new Set<T>();
        /// <summary>
        /// Add a item if it is not contained in the set.
        /// </summary>
        /// <param name="item"></param>
        /// <returns></returns>
        public new int Add(T item)
        {
            if (this.Contains(item))
            {
                return this.IndexOf(item);
            }
            else
            {
                base.Add(item);
                return this.Count - 1;
            }
        }

        /// <summary>
        /// Add a set of items.
        /// </summary>
        /// <param name="items"></param>
        public new void AddRange(IEnumerable<T> items)
        {
            foreach (T item in items)
            {
                this.Add(item);
            }
        }

        public Set<T> SubSet(IList<int> indice)
        {
            Set<T> subset = new Set<T>();
            foreach (int index in indice)
            {
                subset.Add(this[index]);
            }
            return subset;
        }

        public override string ToString()
        {
            return CodeLib.StringHelper.ContactWithDelim<T>(this, ",", "{", "}");
        }

        /// <summary>
        /// Union
        /// </summary>
        /// <param name="A"></param>
        /// <param name="B"></param>
        /// <returns></returns>
        public static Set<T> operator +(Set<T> A, Set<T> B)
        {
            Set<T> sum = new Set<T>();
            sum.AddRange(A);
            sum.AddRange(B);
            return sum;
        }

        /// <summary>
        /// Difference
        /// </summary>
        /// <param name="A"></param>
        /// <param name="B"></param>
        /// <returns></returns>
        public static Set<T> operator -(Set<T> A, Set<T> B)
        {
            Set<T> diff = new Set<T>();
            foreach (T item in A)
            {
                if (!B.Contains(item))
                {
                    diff.Add(item);
                }
            }
            return diff;
        }

        /// <summary>
        /// Intersect
        /// </summary>
        /// <param name="A"></param>
        /// <param name="B"></param>
        /// <returns></returns>
        public static Set<T> operator *(Set<T> A, Set<T> B)
        {
            Set<T> common = new Set<T>();
            foreach (T item in A)
            {
                if (B.Contains(item))
                {
                    common.Add(item);
                }
            }
            return common;
        }
    }
}
